Any book on antebellum US history should cover the Texas question. I'd recommend either What Hath God Wrought by Howe or The Impending Crisis by Potter if you just want broad over views of history during that time period. I'm almost positive both cover Texas at some point. Both are pretty big tomes but well worth the read. I think both won Pulitzer Prizes. The Wikipedia article is largely based on Freehling's The Road to Disunion Vol. I, which is highly regarded, if perhaps showing it's age at this point.

Definitely since 1959 is kind of a late date to pick. There were relatively advanced electronic computers by this time period. In addition, scientists were at least aware of what caused electromagnetic pulses in late '58, though it was not confirmed until '62. The pulses from space would not prevent our confirmation, and may have even sped it up.

I would assume we would just end up shielding any electronic devices made after 1959. The result would likely be much more expensive electronic devices. Radios and Televisions would not be nearly as ubiquitous, and transmission of their signals would be routinely interrupted. It might be easier to just design the devices to turn off every hour in synchronicity with the space-pulse. Other devices would be rarer as well, delaying or preventing the information renaissance we find ourselves in today.

Actually the US only decided to annex Texas after it was revealed that Great Britain was negotiating to pay off their huge war debts if they rejoined Mexico and gave up slavery, both of which they nearly did. The majority of US lawmakers were against it until '44, nearly 12 years after Texas independence.

It really depends on why it never secedes. For it to never revolt the Mexican government would have had to either prevented Austin and other American's from settling in Texas, or placated them. Mexico faced lots of rebellions and civil wars, so its hard to not see people taking advantage of the chaos to rebel in Texas.

If the Spanish had decided to not allow any American settlers into Spain in 1820 they would have likely filtered in illegally and still ended up as the majority of the population by the 1830's, but it might have taken longer and they would have probably been far less organized. Famous leaders like Austin and Houston would have probably stayed in the states rather than travel illegally. The disorganized and secretive settlers would be targeted by Comanche and Apache raiders. The failure of the Mexican government to protect American settlers, no matter how illegal, might cause the American government to intervene as they did in Spanish-Florida against the Seminole in 1816-1819. This would eventually lead to either war, or the selling of the settled parts of Texas to the United States.

If the Spanish do allow settlers, and then make concessions to them, the biggest of which is to allow slavery, then Texas probably becomes more and more autonomous until it is barely connected with Mexico eventually. While they never go to war or declare independence, Texas exists as a totally autonomous state within Mexico.

Can you really call that an invention of the Nazi's? They weren't really in control of Germany until '32, and Hitler wasn't the Chancellor until '33. He did join the Nazi Party in '36, but that may have been because it was the only way to get government funding.